Improvement in the construction of bridges



T. C. FIDLER.

CONSTRUCTION oF BRIDGES.

Patented March 7,1876.

STAT-Es IMPROVEMENTIN THE CONSTRUCTION OF BRIDGES.

Specification forming part of Letters Patent No. l 74,5 l0, dated MarchI7, l87ti application tiled f December 12, 1874.

To all whom it may concern:

. Be it known that I, THOMAS CLAXTON FID- LER, 'ot' Emberton, .in thecounty ot' Bucks, England, civil engineer, have invented Improvements inthe Construction of Suspension- Bridges and Iron Arches, of which thefollowing is a specilcation My said4 invention consists in a method ot'constructingl suspension-bridges whereby the chains are so arranged andbraced as to afford an inexible support to the roadway, and to carry apassing load without distortion; and in order that my said inventionmaybe fully understood I shall now proceed more particularly to describethe same, and for that pur- 4pose shall refer tothe several figures onthe annexed sheet of drawings, the same letters of reference indicatingcorresponding parts in all the corresponding figures.l

a Figure l of my drawings is an elevation of a suspension -bridgeconstructed according to my said invention.

a a are the piers, and b b the land-ties. In the place of a single chainfrom c to h, I employ two chains, (represented by the lines c d e fg hand c z' kfm 7L,) which are attached together, or to the samesaddle,'at"`c and h, and cross each other at f.' The line c i kf is aparabolic curve, and the line f m his `a straight line, whiwch forms atangent to that curve va'afrIn like manner the chain f g h lies ip aparaboliccurve, and the chain c d e f in a straight line, which forms atangent to that ycurve at the point f. The chains are united by thevertical struts d t' e 7s, 8vo., and by the diagonal braces d k 'i e,85o. The roadway r r is attached to the chains by the rods i r k fr, &c.If the half-span cj' is uniformly loaded the load is carried by thechaine i kf m h, which forms aline of equilibrium for that load quiteindependently of what, load there may beA upon the other half-span.V Inlike manner the'chain c d cfg h is in equilibrium under any uniform loadupon the half-span f v h, so that eachchain is under a uniformhorizontal tension throughout its length so long asthe two half-spansare uniformly loaded, though the load on one halt may be greater thanthe load on' the other half, and the braces have no strain upon them.

When either half -span is only partially bow-string rib. "Ihe bracingacting in this way4 increases the strain in certain parts of the chains,and lessens itin otherparts, and I make the sectional area of the chainsproportional to the secant of the angle o'f inclination at its differentparts, just as inA an' ordinary suspension-chain, because the greatesthorizontal strain is the same for every bar of the lower chain, and isnearly equal to the horizontal strain of the upper chain at f, but lessthan the greatest horizontal strain in the upper chains at cfandh. 1

In bridges of large span, Where the live load bears a small proportionto the dead load,

thejgminution ot'-V tension caused by an irregular loading of eitherhalf-.span is not great, and I construct the chains of such bridges inany ordinary method, as shown in Fig. 2, which is a cross-section of theinverted bowstring rib formed by one-half of the bridge. a is the upperchain b, the lower'chain, and c is a vertical strut braced to resistcompression.

1 In bridges where the live load bears a great proportion to the deadload the upper chain may at certain points be thrown into compression.Therefore, in small bridges, I substitute a rigid plate structure inplace of the upper-chain, as shown in the cross-section, Fig. 3, wherethe upper chain is replaced by the plates ct and angle-irons b, whichare capable of resisting either tension or compression. d is the lowerchain, and c is a vertical strut built of plate and angle irons. Thedifterences of strain caused by the said irregular loading are less whenthe upper chain is straight than when ithangs in a curve; therefore Iconstruct all suspension-bridges with the upper chain straight. a

In building arched structures on the same principle the two half-ribs,as seen in Fig. 4, are hinged at the abutments a and c, and hingedtogether lat the crown b. Each halt'- rib has an upper llange, a d b,sharply curved,

. and a lower tia-nge, a e b, less sharply curved,

or straight. The lianges meet at a and at b, and are united in themiddle by a plate or lattice-web h, and the flanges are so arrangedPATENT rFIo-n 'iiange a e b into tension; but, as this is of noconsequence, the lower flange may be curved, and not straight.

Fig. 5 is a cross section ot' an arch-rib of wrought-iron, the upperflange a b and the lower ange d e being built of plate and angle ironunited by the plate or lattice-web c. Fig.

. 6 is across-section of an arch-rib of cast-iron,

in which the flanges a and b and the web c are cast in one piece. Thesuspension bridge may also have the cross-section shown in Figs. 5 or 6,and may be constructed exactly as the arch inverted.

The half-ribs ot' the suspension-bridge are in any case either actuallyor virtually hinged to the piers at c and h, Fig. l, and hinged togetheratf. The upper and lower chains or ijanges may be actually hingedtogether and with the saddle ath, or the two chains may be separa tclyattached to the saddle, as shown in Fig. 7, in which a d is a' bar otlthe upper chain; b c. a bar otf the lower chain, attached by the pins aand b to the saddle-plates e. The pins a and b are placed in the line ofthe bar b c, so that a small angular motion ofthe whole half-rib wouldproduce no sensible strain upon either bar. In the same way the twohalf-ribs may be actually hinged together at j', Fig. l, or the twochains may cross each other, the ilat links of one chain passing betweenthose ot' the other chain; or the upper and lower chain otl eachhalf-rib may be sep-.

arately attached to junction-plates, as shown in Fig. 8, in which p isthe junction-plate, to which are attached the chains a b and e f of theleft half-rib, and the upper chain g h n and lower chain c d o of theright half-rib, the centers b, c, f, and g being arranged in the linesof the bars, or nearly so, in the same way as in Fig. 7. iis a verticalstrut in the right half-rib, and 7c 7i. the diagonal braces, cottered upto an adjusting-plate, m.

I do not desire to claim, broadly, a suspension-bridge constructed withtwo chains attached to the same piers and crossing each other at thecenter; but

1. A suspended or arched structure, in which two half-ribs are jointedtogether' at the center ot' the span, each half-rib consisting of astraight member and a curved member, so arranged that the straightmember of one haltrib torms a tangent to, ora direct continuation ot',the curved member ot' the other half-rib, substantially as described.

2. lIhe two half-ribs, constructed of plate and angle iron,substantially as described, and hinged to each other and to the piers orsaddles, as set forth.

In witness whereof I have signed my name to this specification in t-hepresence of two subscribing witnesses.

T. C. FIDLER.

